With the right peripherals, a lot. On my 1980 TRS-80 Color Computer I can write documents and save them to tape, print them, or send the text over serial to a m

With the right peripherals, a lot. On my 1980 TRS-80 Color Computer I can write documents and save them to tape, print them, or send the text over serial to a modern computer. (It can also function as a serial terminal, but that's kind of cheating.) It boots to BASIC, no disks required (but can run a version of DOS if a drive is present). There's some early database/PIM software, home automation controllers, graphics tablets, and of course games. With full access to the serial and joystick ports, it's essentially able to function as a microcontroller, though I'll admit I mostly just use mine for writing, drawing, and games.